Modified strong-dipole proton-coupling model for hydrogen-bonded ferroelectrics

The ferroelectric phase transition of hydrogen-bonded ferroelectrics, KH2PO4-type, was investigated by employing a model of the strong-dipole proton coupling (SDPC). Besides the change of the dipolar component along the c axis, which was earlier considered within the original SDPC model, the continuous three-dimensional changes of the dipole were introduced in the model. The influence of these changes on the ferroelectric phase transition was examined by employing Monte Carlo calculation. It is shown that the experimental data for the spontaneous polarization along the polar c axis are better described with such a modified SDPC model in the vicinity of the ferroelectric transition temperature, T-C, than with the original SDPC model. The additional superiority of the modified model compared to the original is the ability to describe experimentally detected discontinuity in the transversal dielectric constant around T-C. It is also demonstrated that the modified SDPC model reduces the gap between the previously calculated and the experimentally detected T-C of KD2PO4 ferroelectric.